Re: anyone ever done multicast AF_UNIX sockets?

Terje Eggestad
2003-03-03T23:25:26Z

The latency I belive, a 25% increase don't matter all that much. (
routinely send meesages sub micro second.

that tcp BW is ridiculus low, make sure that you run with with good
sized socket buffers, and that tcp windowing is enabled.

But then again, if you want to send much data fast between processes, a
stream socket is a pretty bad idea anyway.
A) shm
b) mmap a file, write into it, and send the filenake to the other side,
then mmap it there.

Don't underestemate the BW of a fedex'ed tape.

TJ

On Mon, 2003-03-03 at 22:32, Chris Friesen wrote:
Terje Eggestad wrote:
> On Mon, 2003-03-03 at 19:56, David S. Miller wrote:

> TCP bandwidth is slightly faster than AF_UNIX bandwidth on my
> sparc64 boxes for example.
>
> I've seen that their are the same on linux.I tried to to do AF_UNIX
> instead of AF_INET internally to boost perf, but to no avail. Makes you
> suspect that the loopback device actually create an AF_UNIX connection
> under the hood ;-)

On my P4 1.8GHz, AF_INET vs AF_UNIX looks like this:

*Local* Communication latencies in microseconds - smaller is better
-------------------------------------------------------------
Host OS 2p/0K Pipe AF UDP RPC/ TCP RPC/ TCP
ctxsw UNIX UDP TCP conn
--------- ------- ----- ----- ---- ----- ----- ----- ----- ----
pcard0ks. 2.4.18- 1.740 10.4 15.9 20.1 33.1 23.5 44.3 72.7
pcard0ks. 2.4.18- 1.560 10.6 16.0 23.4 38.1 36.1 44.6 77.4

*Local* Communication bandwidths in MB/s - bigger is better
-----------------------------------------------------------
Host OS Pipe AF TCP File Mmap Bcopy Bcopy Mem Mem
UNIX reread reread (libc) (hand) read write
--------- ------- ---- ---- ---- ------ ------ ------ ------ ---- -----
pcard0ks. 2.4.18- 650. 677. 151. 721.9 958.0 290.8 288.8 955. 418.4
pcard0ks. 2.4.18- 379. 701. 163. 714.8 949.5 289.5 288.5 956. 420.5

On this machine at least, UDP latency is 25% worse than AF_UNIX, and TCP
bandwidth is about 22% that of AF_UNIX.

Chris

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Terje Eggestad mailto:terje.eggestad@scali.no
Scali Scalable Linux Systems http://www.scali.com

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